NASA - National Aeronautics and Space Administration

The PUTLS comprises three individual instruments for the measurement of aerosol number size distribution in the upper troposphere and lower stratosphere: a Nucleation Mode Aerosol Size Spectrometer (NMASS), an Ultra-High Sensitivity Aerosol Spectrometer (UHSAS), and a Portable Optical Particle Spectrometer (POPS). These instruments, along with a Passive, Near-Isokinetic Inlet for sampling atmospheric particles from a fast-moving aircraft, provide a measurement of the UT/LS particle size distribution from 4 to 3000 nm diameter. Aerosol microphysical measurements in the UT/LS are integral to understanding the chemical and radiative processes that control the Earth’s climate, and PUTLS provides data for investigation of topics ranging from new particle formation to long range transport of dust and fine volcanic ash.

Two instruments,a nucleation-mode aerosol size spectrometers (NMASS; Williamson et al., 2018), and an ultra-high sensitivity aerosol spectrometers (UHSAS; Kupc et al., 2018) comprise the AMP package for ACCLIP. The AMP package provides particle size distributions with up to one-second time resolution for dry aerosol particles between 0.003 and 1.5 µm in diameter. Details of methods, uncertainties, and data products from the AMP package are in Brock et al. (2019).

During ATom, the instruments were used to investigate how particles in the remote atmosphere influence climate by examining the origin of small particles in the remote atmosphere and their growth to sizes where they can affect clouds and the sources, characteristics, and distribution of soil dust and sea-spray particles, and 3) the importance long-range transport from human and natural sources on background aerosol properties.

4STAR (Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research; Dunagan et al., 2013) is an airborne sun-sky spectrophotometer measuring direct solar beam transmittance (i.e., 4STAR determines direct solar beam transmission by detecting direct solar irradiance) and narrow field-of-view sky radiance to retrieve and remotely sense column-integrated and, in some cases, vertically resolved information on aerosols, clouds, and trace gases. The 4STAR team is a world leader in airborne sun-sky photometry, building on 4STAR’s predecessor instrument, AATS-14 (the NASA Ames Airborne Tracking Sun photometers; Matsumoto et al., 1987; Russell et al. 1999, and cited in more than 100 publication) and greatly expanding aerosol observations from the ground-based AERONET network of sun-sky photometers (Holben et al., 1998) and the Pandora network of ground-based direct-sun and sky spectrometer (e.g, Herman et al., 2009).

4STAR is used to quantify the attenuated solar light (from 350 to 1650 nm) and retrieve properties of various atmospheric constituents: spectral Aerosol Optical Depth (AOD) from ultraviolet to the shortwave infrared (e.g., LeBlanc et al., 2020, Shinozuka et al., 2013); aerosol intensive properties - Single Scattering Albedo (SSA; e.g., Pistone et al., 2019), asymmetry parameter, scattering phase function, absorption angstrom exponent, size distribution, and index of refraction; various column trace gas components (NO₂, Ozone, Water Vapor; e.g., Segal-Rosenheimer et al., 2014, with potential for SO₂ and CH₂O); and cloud optical depth, effective radius and thermodynamic phase (e.g., LeBlanc et al., 2015).

Some examples of the science questions that 4STAR have pursued in the past and will continue to address:

• What is the Direct Aerosol Radiative Effect on climate and its uncertainty? (1)
• How much light is absorbed by aerosol emitted through biomass burning? (1)
• How does heating of the atmosphere by absorbing aerosol impact large scale climate and weather patterns? (1)
• How does aerosol spatial consistency of extensive and intensive properties compare? (2)
• How does the presence of aerosol impact Earth’s radiative transfer, with co-located high concentration of trace gas? (3, 5)
• What is the impact of air quality from long-range transport of both aerosol particulates and column NO2 and Ozone, and their evolution? (3, 6)
• What are the governing properties and spatial patterns of local and transported aerosol? (1)
• How are cloud properties impacted near the sea-ice edge? (4)
• In heterogeneous environments where clouds and aerosols are present, how much solar radiation is impacted by 3D radiative transfer? And how does that impact the aerosol properties? (5)

(1) ORACLES: Zuidema et al., doi:10.1175/BAMS-D-15-00082.1., 2016; LeBlanc et al., doi:10.5194/acp-20-1565-2020, 2020; Pistone et al., https://doi.org/10.5194/acp-2019-142, 2019;Cochrane et al., https://doi.org/10.5194/amt-12-6505-2019, 2019; Shinozuka et al., https://doi.org/10.5194/acp-20-11275-2020, 2020; Shinozuka et al., https://doi.org/10.5194/acp-20-11491-2020, 2020
(2) KORUS-AQ:  LeBlanc et al., doi:https://doi.org/10.5194/acp-22-11275-2022, 2022

(3) KORUS-AQ: Herman et al., doi:10.5194/amt-11-4583-2018, 2018
(4) ARISE: Smith et al., https://doi.org/10.1175/BAMS-D-14-00277.1, 2017; Segal-Rosenheimer et al., doi:10.1029/2018JD028349, 2018
(5) SEAC4RS: Song et al., doi: 10.5194/acp-16-13791-2016, 2016; Toon et al., https://doi.org/10.1002/2015JD024297, 2016
(6) TCAP: Shinozuka et al., doi:10.1002/2013JD020596, 2013; Segal-Rosenheimer et al., doi:10.1002/2013JD020884, 2014

The GV Scanning Mobility Particle Sizer (SMPS) measures the particle size distribution over the mobility diameter range of 3 to 500 nm (pressure-dependent). It consists of two components: an electrostatic classifier (EC) and a condensation particle counter (CPC). The EC samples aerosol-laden ambient air, places a well-defined charge distribution on the particles, and then selects a narrow range of particle “mobility diameter” (approx. equal to cross-sectional area-to-charge ratio) using a differential mobility analyzer (DMA). The selected diameter can be scanned by a time-varying high voltage applied to the DMA; following this particles are counted by the CPC. The total scan time and the number of counting intervals, the latter of which determines the number of diameter bins in the size distribution, are selected based on ambient particle concentrations and altitude. The raw data (particle counts over each counting interval as a function elapsed time during the linear diameter scan) is mathematically inverted during post-processing to obtain the particle size distribution.

The UHSAS is an optical-scattering, laser-based aerosol particle spectrometer for sizing particles in the 0.06 – 1 μm range. The instrument counts particles in up to 100 user-specified sizing bins, with a resolution as fine as 1 nm/bin. This high sensitivity makes the UHSAS ideal for aerosol research and filter testing.

A laser illuminates particles, which scatter light that is then collected by two pairs of Mangin optics. One pair of optics images onto a highly sensitive avalanche photodiode (APD) for detecting the smallest particles. The other pair images onto a low-gain PIN photodiode for detecting particles in the larger size range of the instrument. Each detector is amplified in a current-to-voltage stage that feeds into the analog electronics system. The amplification allows the system to detect particles as small as 60 nm.

Langley Aerosol Research Group Experiment (LARGE).  The "classic" suite of instrumenation measures in-situ aerosol micrphysical and optical properties. The package can be tailored for specific science objectives and to operate on a variety of aircraft. Depending on the aircraft, measurments are made from either a shrouded single-diffuser "Clarke" inlet, from a BMI (Brechtel Manufacturing Inc.) isokinetic inlet, or from a HIML inlet. Primary measurements include:

1.) total and non-volatile particle concentrations (3nm and 10nm nominal size cuts),
2.) dry size distributions from 3nm to 5µm diameter using a combination of mobilty-optical-aerodynamic sizing techniques,
3.) dry and humidified scattering coefficients (at 450, 550, and 700nm wavelength), and
4.) dry absorption coefficients (470, 532, and 670nm wavelength). 

LARGE derived products include particle size statistics (integrated number, surface area, and volume concentrations for ultrafine, accumulation, and coarse modes), dry and ambient aerosol extinction coefficients, single scattering albedo, angstrom exponent coefficients, and scattering hygroscopicity parameter f(RH).

1) Time of Flight Aerosol Mass Spectrometer (ToF-AMS)

Total and single particle characterization of volatile aerosol ionic and organic components (50-700nm). Uncertainty depends on species and concentration.

2) Single Particle Soot Photometer (SP2)

Single particle measure of BC (soot) mass in particles and determination of mixed particle size and non-BC coating using laser scattering and incandescence. 70-700nm. Single particle counting up to 10,000 per sec.

3) A size-resolved thermo-optic aerosol discriminator (30 s avg.):

Aerosol size distribution from 0.12 up to 7.0 μm, often where most aerosol mass, surface area and optical effects are dominant. Uses a modified Laser Optical Particle Counter (OPC) and computer controlled thermal conditioning system is used upstream (airstream dilution dried). Characterizes aerosol components volatile at 150, 300 and 400C and refractory aerosol at 400C (sea salt, dust and soot/flyash). (Clarke, 1991, Clarke et al., 2004). Uncertianty about 15%

4) Condensation Nuclei - heated and unheated (available at 1Hz)

Two butanol based condensation nuclei (CN) counter (TSI 3010) count all particles between 0.01-3.0 um. Total CN, refractory CN (those remaining at 300C after sulfate is removed) and volatile CN (by difference) are obtained as a continuous readout as a fundamental air mass indicator (Clarke et al. 1996). Uncertainty ~ 5%.

5) Aerodynamic Particle Sizer – (APS-TSI3320) – (<5min/scan)

To further characterize larger “dry” particles, including dust, an APS is operated which sizes particles aerodynamically from 0.8 to 20 μm into 50 channels. Uncertainty~10%.

6) Differential Mobility Analyzer with thermal conditioning – (<3 min/scan)

Volatility tandem thermal differential mobility analyzer (VTTDMA) with thermal analysis that provides size information (mass, surface area, number distributions) and their state of mixing over the 0.01 to 0.3μm size range (Clarke et al., 1998, 2007) for sampling times of about 1-3 minutes. Uncertainty ~10%

7) Nephelometer (10-7 m-1 detection for 60s avg., recorded every 1 sec.)

A 3 wavelength nephelometer (450, 550, 700nm) is used for total scattering and submicrometer scattering values using a Radiance Research single wavelength nephelometer (and thereby coarse dust scattering by difference).

8) Two Particle Soot Absorption Photometers (PSAP-Radiance Research; detection <0.1μg m-3 for 5 min. avg. )

The PSAP is used to quantify the spectral light absorption coefficient of the total and submicron aerosol (eg. soot, BC) at three wavelengths (450, 550, 660nm).

9) Humidity Dependent Light-Scattering (10-6 m-1 detection for 60s avg.; recorded every 1 s)

Two additional Radiance Research single-wavelength nephelometers are operated at two humidities (high/low) to establish the humidity dependence of light scattering, f(RH).